Re: Review remove {join,from}_collapse_limit, add enable_join_ordering

On Thu, Jul 16, 2009 at 4:16 PM, Tom Lane<tgl@sss.pgh.pa.us> wrote:
> However, I do observe that this seems a sufficient counterexample
> against the theory that we can just remove the collapse limits and let
> GEQO save us on very complex queries.  On my machine, the example query
> takes about 22 seconds to plan using CVS HEAD w/ all default settings.
> If I set both collapse_limit variables to very high values (I used 999),
> it takes ... um ... not sure; I gave up waiting after half an hour.

What's the point of GEQO if it doesn't guarantee to produce the
optimal plana and *also* doesn't guarantee to produce some plan, any
plan, within some reasonable amount of time? Either we need to fix
that or else I don't see what it's buying us over our regular planner
which also might not produce a plan within a reasonable amount of time
but at least if it does it'll be the right plan.

--
greg
http://mit.edu/~gsstark/resume.pdf